Process for producing crimped polyester filaments

ABSTRACT

A process for producing polyester filaments having high Young&#39;&#39;s modulus and excellent crimps, which comprises heat-treating a bundle of drawn filaments of linear polyester in which at least 85 mole percent of the recurring units consist of ethylene terephthalate, at a temperature of 135* to 240*C. under a tension of at least 0.3 g/denier, feeding the filaments to the nip rollers of a stuffer box while maintaining the filaments at a temperature at least 10*C. lower than the heat-treating temperature and between 100* and 140*C. under a tension of at least 0.1 g/denier, crimping the filaments in the stuffer box, and then with-drawing the filaments from the stuffer box.

United States Patent [19 1 Izawa et al.

[ 1March 13, 1973 PROCESS FOR PRODUCING CRIMPED POLYESTER FILAMENTSInventors: Nobuharu Izawa; Munetsugu Kikuyama; Hiroshi Toyoshima; RyujiYamamoto, Yasuhiro Murase; all of Matsuyama, Japan [73] Assignee: TeijinLimited, Osaka, Japan [22] Filed: May 4, 1971 [21] Appl. No.: 140,209

UNITED STATES PATENTS l/l97l Buschmann et al. ..28/l .6

Primary Examiner-Louis K. Rimrodt Attorney-Sherman & Shalloway [57]ABSTRACT A process for producing polyester filaments having high Youngsmodulus and excellent crimps, which comprises heat-treating a bundle ofdrawn filaments of linear polyester in which at least mole percent ofthe recurring units consist of ethylene terephthalate, at a temperatureof to 240C. under a tension of at least 0.3 g/denier, feeding thefilaments to the nip rollers of a stuffer box while maintaining thefilaments at a temperature at least 10C. lower than the heattreatingtemperature and between 100 and C. under a tension of at least 0.1g/denier, crimping the filaments in the stuffer box, and thenwith-drawing the filaments from the stuffer box.

8 Claims, 1 Drawing Figure PROCESS FOR PRODUCING CRIMPED POLYESTERFILAMENTS This invention relates to a process for producing polyesterfilaments having both high Youngs modulus and excellent crimps.

Previously, polyester type fibers have been widely utilized in the formof staple fibers after being given mechanical crimps. Usually, aftermelt spinning, the polyester fibers obtained are drawn, and thensubjected to heat-treatment while allowing shrinkage to take place inorder to improve their dimensional stability, but the Youngs modulus ofthe polyester fibers thus obtained is considerably lower than that ofnatural cotton fibers. Therefore, there has been a demand forexcellently crimped polyester fibers still having a Youngs modulus equalto, or higher than, natural cotton fibers. In an attempt to produce suchpolyester fibers, a method has been developed in which after meltspinning, the resulting filaments are drawn in multistages at thehighest possible draw ratios to form polyester filaments having a highYoungs modulus, and then the filaments are subjected to a crimpingtreatment. However, when such filaments are crimped, for instance, by astuffer crimper, there is the defect that the filaments are moredifficult to crimp with increasing Youngs modulus. This is due to thefact that the deformation of the filaments is difficult to cause becauseof the high Youngs modulus, and the filaments are not sufficiently bent.One method of removing this defect is proposed in Japanese PatentPublication No. 22028/64 which discloses a method wherein the filamentsare preheated before the crimping operation so as to reduce the Youngsmodulus and accordingly to make them easy to crimp. Another method ofthis kind is disclosed in Japanese Patent Publication No. 14017/64, inwhich after heat-treatment under tension, the filaments are cooled tobelow the minimum crystallization temperature (usually 90-95C. forpolyester fibers) to retard crystallization. These methods havecontributed to some extent to the improvement of the crimpability of thepolyester fibers of high Youngs modulus. But the crimpability is stillinferior to that of polyester filaments having low Youngs modulus, andimprovement is still required.

It is therefore an object of this invention to provide a process forproducing polyester filaments having high Youngs modulus and excellentcrimps which properties have been somewhat inconsistent with each other.

According to this invention, a process is provided for producingpolyester filaments having high Youngs modulus and excellent crimps,which comprises heattreating a bundle of drawn filaments of asubstantially linear, fiber-forming, high-molecular-weight polyesterhaving at least 85 mole percent of the recurring units consisting ofethylene terephthalate, at a temperature of 135 to 240C. under a tensionof at least 0.3 g/denier, feeding the filaments to nip rollers of astuffer crimper while maintaining the filaments at a temperature atleast C. lower than the heat-treating temperature and between 100 and140C. under a tension of 0.1 g/denier or more, crimping the filaments inthe stuffer box and then withdrawing the filaments therefrom.

The invention will be described in greater detail below with referenceto the accompanying drawing which is a schematic side elevation of anapparatus for performing one embodiment of the process of the presentinvention.

The polyester filaments used in the invention are those obtained from asubstantially linear, fibenforming, high-molecular-weight polyester inwhich at least mole percent of the recurring units consist of ethyleneterephthalate. The polyester polymer may contain less than 15 molepercent of an acid component such as isophthalic acid or adipic acid, analcohol component such as propylene glycol, or a branching agent as acopolymerzable component.

. According to the process of the present invention, the polyesterdescribed above is melt-spun by an ordinary method to form undrawnfilaments and then the undrawn filaments are hot drawn by a known methodto form drawn filaments. Preferably, the drawing is carried out inmulti-stages, and by this method highly oriented filaments can beobtained. The preferred total draw ratio used at this time is 3.5 to6.0. The drawn filaments so obtained are heat treated at a temperatureof to 240C. under a tension of at least 0.3 g/denier to producepolyester filaments having high Youngs modulus which are highly orientedand crystallized. 1f the heat-treatment temperature is lower than 135C,the Youngs modulus of the resulting crimped filaments is notsufficiently high. On the other hand, heat-treating temperatures above240C. cause localized melting of the filaments, and result in themelt-adhesion of the filaments with one another. Such filaments are ofcourse not viable for practical purposes.

The preferred heat-treating temperature is from 150 to 230C. The tensionto be exerted on the filaments at the time of heat-treatment should beat least 0.3 g/denier. If the tension is lower than 0.3 g/denier, evenheattreatment at temperatures within the above-specified range does notgive filaments of sufficiently high Youngs modulus, and there is theaccompanying defeet of the difficulty of crimping such filaments. Thepreferred lower limit of the tension is 0.5 gldenier, and the preferredupper limit is 3.5 g/denier.

The heat-treated polyester filaments are then cooled, and then fed tonip rollers of a stuffer box while the filaments immediately beforeentry into the nip rollers are maintained at a temperature at least 10C,preferably at least 20C. lower than the heat-treatment temperature andbetween 100 and C. and under a tension of at least 0.1 g/denier. Withinthe stuffer box, the filaments are crimped in a manner known per se. Thecrimped filaments are withdrawn from the stuffer box in accordance witha customary method. Coveniently, the temperature adjustment of thefilaments is accomplished by using conventional heating rollers. Thetemperature of the filaments generally drops to some extent during thetravelling of the filaments between the last heating roller and the niprollers of the stuffer crimper. In the process of the present invention,therefore, it is necessary to set the temperature of the heating rollersso that the temperature of the filaments immediately before entry intothe nip rollers is within the range specified above. The extent oftemperature drop of the filaments travelling between the last heatingroller and the nip rollers depends upon such factors as the differencebetween the temperature of the last heating roller and the ambienttemperature or the travelling time (usually less than several seconds),but once the operational conditions are set at constant values, theextent of the temperature drop also becomes substantially constant.Therefore, in actual operation, the temperature of the filamentsimmediately before entry into the nip rollers is measured by a propersurface temperature measuring device, and the tempreature of the heatingroller is set so that this measured temperature is within thetemperature specified in the present invention.

The critical point of the process of the invention is that the polyesterfilaments heat-treated under tension are cooled to a temparature atleast C. lower than the heat-treating temperature and between 100 and140C. and placed under a tension of at least 0.1 g/denier, and in thisstate the filaments are fed to the nip rollers of the stuffer crimper.In particular, the novel feature of the invention consists in theemployment of the above-described feed conditions in relation to thecondition of heat treatment under tension mentioned above.

When the polyester filaments are stuffed into the stuffer box via thenip rollers, they are inevitably released from tension within thestuffer box. As is generally known, when filaments are placed undertension, free shrinkage is restrained by the tension, but when thefilaments are placed in a tension free state, free shrinkage developsabruptly and easily; consequently, the orientation of the filaments isrelaxed and their Youngs modulus is reduced. Such a relaxation of theorientation which occurs within the stuffer box is supposed to be higherwith increasing temperature of the filaments fed into the stuffer box.It has been found that in order to prevent the high Youngs modulus ofthe polyester filaments attained by the heat-treatment specified in thepresent invention, from being reduced by the relaxation of theorientation described above, it is very effective to feed the filamentsto the nip rollers of a stuffer box while maintaining the filaments at atemperature at least 10C., preferably at least C., lower than theheattreatment temperature.

For the same reason as mentioned above, too high a temperature of thefilaments at the entry into the stuffer box is undesirable formaintaining a high' Youngs modulus. It is therefore necessary to adjustthe temperature of the filaments to be fed to the nip rollers by theprocess of the invention to 140C. or below. On the other hand, from thestandpoint of the ease of crimping, filaments to be crimped shouldconvenietly have the highest possible temperature and be softened. Sincethe filaments to be crimped in the invention have high Youngs modulusand are highly oriented and crystallized, the softening of the filamentsplays an especially important role for imparting good crimps to thefilaments. Therefore, in the process of the invention, the temperatureof the filaments to be fed to the nip rollers should be adjusted to100C. or above, preferably 1 10C. or above.

It is further very important in the process of the present inventionthat the polyester filaments heattreated under tension should be fed tothe nip rollers of the stuffer box while maintaining them under atension of at least 0.1 g/denier without releasing the tension. In theconventional methods, it was common practice to release the tensionoffilaments and place them in a tension-free state or place them under aslight tension, and feed the filament into the stuffer box in such atensionfree state. According to these methods, the fiber-structure ofthe filaments is stabilized incident to their shrinkage in a state oflow tension. On the other hand, the degree of orientation is reduced,and the Youngs modulus of the filaments is decreased. It is due to thisstructural stabilization by the shrinkage that the filaments becomedifficult to crimp. The novel feature of the process of the presentinvention is that the filaments can be given both excellent crimps and ahigh level of Youngs modulus by placing the heat-treated filaments undertension until they are fed into the stuffer box and at the same timemaintaining the filaments immediately before entry into the nip rollersat the specific temperature described above. In the process of thepresent invention, the preferredtension to be exerted on the filamentsto be fed to the nip rollers is at least 0.2 g/denier. The upper limitof the tension is difficult to set, but can be defined as the tensionsuch that the nip rollers of the stuffer box can grip the filamentssufficiently without slippage. Usually, the upper limit of the tensionis about 1.0 g/denier. The stuffer crimper used in the invention may beof any type known and used in theart.

Referring to the accompanying drawing, undrawn filaments extruded from amelt-spinning apparatusof the conventional type (not shown) are drawn byfeed rollers (not shown), a heating device (not shown) such as hot pin,hot plate, or hot bath and a pair of draw rollers l and 1' to producedrawn filaments 2. The drawn filaments 2 which have left a pair of drawrollers l and l, are heat-treated under tension by rollers 3,4,5,6 and 7heated at 240C. The filaments are then passed over heating rollers 8 and9 the temperature of which is set so that the temperature of thefilaments immediately before entryinto between nip rollers 11 and 11' isat least 10C. lower than the heat-treating temperature and between 100and C., and cooled to some extent. The filaments are then passed over aguide roller 10, and then fed between a pair of nip rollers 11 and 11'and then stuffed into a stuffer box 12 and crimped therein. Thereafter,the crimped filaments are withdrawn from the stuffer box 12, and fedonto a net conveyor 13. If desired, the filaments are subjected toheat-treatment in a relaxed state. Then the filaments are transferred toa cutter (not shown), and cut to staple fibers. It is preferred that thedraw rollers l and l and the heating rollers 3 to 9 are alldriven at thesame peripheral speed. The peripheral speed of the nip rollers 11 and11' may be 95-105 percent of that of the heating roller 9 so that thetension on the filaments between the guide roller 10 and the nip rollersis 0.1 g/denier or above.

It is preferred that one or more of the heating rollers 3 to 9 should beused for cooling purposes. The number of the cooing rollers is properlychosen. Hot plates or hot vapor may also be used as the heating orcooling medium. The use of rollers is advantageous in that a largerlength of contact between the roller and the filaments can be obtainedwith the need for a smaller space.

The following Examples will illustrate the present invention.

EXAMPLE 1 A 500,000 denier undrawn polyethylene terephthalate tow wasdrawn at a draw ratio of 3.80 at 70C. in a It is clear from the resultsgiven in Table l that polyester filaments having sufficiently highYoungs modulus cannot be obtained at temperatures below 135C., and whenthe heat-treatment temperature is first stage, and at a draw ratio of atin 5 250C, the undesirable melt-adhesion of the individual a secondstage The tow was then passed over heating filaments occurs. The resultsof the comparison 2, 3 rollers of the type shown in the accompanying drag, and 4 show that unless the temperature of the filaments and then fedinto a stuffer crimpe Wher t as immediately before entry into thecrimper is kept at crimped. The heating rollers 3 to 7 were used forheatleast C. lower than the heat-treating temperature treating purposes,and the heating rollers 8 and 9, for 10 and between 100C. and 140C.,both the crimpability cooling purposes. The experiments were performedat and Youngs modulus cannot be improved at the same varying rollertemperatures. The tension of the tow was time. 1.5 g/denier between theroller 3 and the cooling roller 9, and 1.0 g/denier between the guideroller 10 and the EXAMPLE 2 nip rollers 11 and 11'. The results areshown in Table 1. C im ed l e ter filaments were produced under Thepercentage crimp, the number of-crimps, and the same conditions as usedin the preparation of the Youngs modulus were measured by the followingfilaments in Run 5 of Example 1 except that the tension methods. of theyarn was the same both at the time of the heattreatment under tensionand at the time of cooling PERCENTAGE CRIMP treatment, and this tensionwas varied as shown in Table 2 below. The properties of the filamentsobtained The specimen filament ofa given length (a) is placed are shownin Table 2 below. under an initial load of 2 mg/denier. Then, a load of50 mg/denier is exerted on the filament, and the length (b) T bl 2 ofthe filament is measured after the lapse of P seconds. The percentagecrlmp 1s expressed by: Tension of Number of gg Young,s Run Nos. the yarncrimps per camp lrtntlxduh s d 25 m X 100 (Percent) s-1 e) l5. 6 g 731i30 5-2 0.6 12.6 14,2 680 54 0.4 13.0 13.3 600 NUMBER OF CRIMPSComparison 0.25 12.8 11.6 510 The g i a g 3 It is seen from the resultsshown in Table 2 that the i 5. 2 emler s 5 tension of the yarn at thetime of the heat-treatment Va 9 y 6 Va 0 gwes t e must be at least 0.3g/denier, preferably at least 0.5 number of cr1mps per 25 mm smce thenumber of g/denier, and when the tension is reduced to 0.25 g/debuckllngpomts 1s tw1ce as great as that ofcrlmps. flier the Youngis modulusdecreases, and filaments having high Youngs modulus cannot be obtained.YOUNG S MODULUS EXAMPLE 3 The stress-strain curve of the specimenfilament is Crimped polyester filaments were produced under recorded byan lnstron tensile tester, and the Youngs the Same conditions as Shownin Runs NOS. 1 and 7 in modulus is calculated from the inclination ofthe tan- Example 1 except that the tension f the yam between gem whichProvides the maximum gradient oh the the heating roll 9 and the niprollers of the crimper was curvechanged as follows: (a) reduced to 0.5g/denier, (b) The temperature of the filaments at the inlet of thereduced to 2 g/denier, (c) reduced to 1 g/denier, crimper as shown inTable l was obtained by measuring 1) d d to 0 05 /d nier, nd (e) reducedto 0.05 the temperature of the filaments immediately before g/denier andthe elevated to 5 g/denieL The entry to the nip rollers of the crimperusing a surface cemage rimp and the number of crimps of each of thetemperature measuring instrument type PIP-4F filaments obtained weremeasured and shown in Table produced by Anritsu Meter Mfg., Co. 3

TABLEI Temperature Temperature Temperature of heating eating ofthe towNumber 01 Percentage Youngs rollers 3 to 7 rollersBand 9 at the inletcrlmps per crimp modulus Run numbers 0.) C.) of crimper .5 cm. (percent)(kg/mm?) Comparison 1. 125 115 111 13. 0 13. 0 550 1 135 115 110 12. s14. 3 710 2 135 125 119 13.1 12.3- 660 Comparison 2 135 135 129 12.912.1 530 com arisons 150 87 13.2 10.3 720 3 150 102 13.1 12.9 750 4" 150104 12. 9 1a. 9 150 5. 150 113 1:1. 3 15.8 780 a... 170 130 121 13.015.4 860 1 170 13s 13. 1 14. 0 s50 Cmnparison 4 170 147 13. 0 12.4 570 a230 130 120 12.8 12. 4 s30 Comparison 5 250 130 118 Melt adhesionoccurred partly TABLE 3 Run No. 1 Run N0. 2

Heat-treating temperature Cooling temperature Number Percentage Young'sNumber Percentage Youngs of crimps crimp modulus of crimps crimpsmodulus Properties per 2.5 cm. (percent) (kgJmmfl) per 2.6 cm. (percent)(kg/mm!) The results shown, in Table deinh'iihTtFafiwfieh Iff'ififii's"tfciafih'i, wherein the upper limit of the tension of theyarn is once reduced as in (d) and (e), the relaxation of the strain ofthe filaments rapidly proceeds, and it becomes difficult to impart goodcrimps to the filaments and at the same time, the Youngs modulus isreduced.

What we claim is:

l. A process for producing polyester filaments hav- 7 ing high Youngsmodulus and excellent crimps, which comprises heat-treating a bundle ofdrawn filaments of a substantially linear, fiber-forming,high-molecularweight polyester in which at least 85 mole percent of therecurring units consist of ethylene terephthalate, at a temperature of135 to 240C. under a tension of at least 0.3 g/denier; feeding thefilaments to the nip rollers of a stuffer box while maintaining thefilaments at a temperature at least 10C. lower than the heat-treatingtemperature and between 100 and 140C. under a tension of at least 0.1g/denier; crimping the filaments in the stuffer box; and thenwithdrawing the filaments from the stuffer box.

the tension during the heat-treatment is 3.5 g/denier.

3. A process of claim 1, wherein the lower limit of the tension duringthe heat-treatment is 0.5 g/denier.

4. A process of claim 1, wherein the treating temperature in theheat-treatment step is to 230C.

5. A process of claim 1, wherein the filaments heattreated under tensionare fed to the nip rollers with the temperature of the filamentsmaintained at at least 20C. lower than the heat-treating temperature.

6. A process of claim 1, wherein the lower limit of the temperature ofthe filaments fed to the nip rollers is 1 10C.

7. A process of claim 1, wherein the upper limit of the tension of thefilaments fed to the nip rollers is 1.0 1

g/deier.

8. A process of claim 1, wherein the lower limit of the tension of thefilaments fed to the nip rollers is 0.2 g/denier.

1. A process for producing polyester filaments having high Young''smodulus and excellent crimps, which comprises heat-treating a bundle ofdrawn filaments of a substantially linear, fiber-forming,high-molecular-weight polyester in which at least 85 mole percent of therecurring units consist of ethylene terephthalate, at a temperature of135* to 240*C. under a tension of at least 0.3 g/denier; feeding thefilaments to the nip rollers of a stuffer box while maintaining thefilaments at a temperature at least 10*C. lower than the heat-treatingtemperature and between 100* and 140*C. under a tension of at least 0.1g/denier; crimping the filaments in the stuffer box; and thenwithdrawing the filaments from the stuffer box.
 2. A process of claim 1,wherein the upper limit of the tension during the heat-treatment is 3.5g/denier.
 3. A process of claim 1, wherein the lower limit of thetension during the heat-treatment is 0.5 g/denier.
 4. A process of claim1, wherein the treating temperature in the heat-treatment step is 150*to 230*C.
 5. A process of claim 1, wherein the filaments heat-treatedunder tension are fed to the nip rollers with the temperature of thefilaments maintained at at least 20*C. lower than the heat-treatingtemperature.
 6. A process of claim 1, wherein the lower limit of thetemperature of the filaments fed to the nip rollers is 110*C.
 7. Aprocess of claim 1, wherein the upper limit of the tension of thefilaments fed to the nip rollers is 1.0 g/deier.